This invention relates to an ignition timing control apparatus for an internal combustion engine, and particularly, it relates to an apparatus for suppressing a knocking produced in an internal combustion engine.
In general, the efficiency of an internal combustion engine increases when its ignition timing is set near to a minimum advance for best torque (which will be hereinafter abbreviated as "MBT").
However, when the ignition timing of the engine excessively approaches the MBT, a knocking condition occurs, whereby the engine is damaged. Thus, an ignition timing control apparatus which detects knocking in the engine and which controls the ignition timing to suppress the knocking has been recently developed and employed.
Particularly in conventional engines having superchargers, the above-described ignition timing control apparatuses have been frequently mounted for the purpose of protecting the engine by preventing excessive knocking from occurring, increasing the power of the engine and for optimizing fuel consumption.
A conventional apparatus of this type will be specifically described with reference to the drawings.
FIG. 1 shows a conventional ignition timing control apparatus of this type. Only a signal component of frequencies corresponding to a knocking of an output of an acceleration sensor 1, mounted on an internal combustion engine, for detecting the vibration acceleration of the internal combustion engine is passed through a frequency filter 2, and a noise signal which disturbs the detection of the knocking signal in the output signal from the frequency filter 2 is interrupted by an analog gate 3. The analog gate 3 is controlled to be opened or closed by a gate timing controler 4 in response to the occurrence of the disturbing noises. The output signal of the analog gate 3 is fed to a noise level detector 5 for detecting the level of a mechanical vibration noise of the engine except for the knocking time. The output of the analog gate 3 and the output voltage of the noise level detector 5 are applied to a comparator 6, which compares both outputs, and outputs a knocking detection pulse depending on the magnitude of both input signals. The output from the comparator 6 is integrated by an integrator 7, which thus outputs an integrated voltage corresponding to the level of knocking. A phase shifter 8 displaces the phase of a reference ignition signal in response to the output signal from the integrator 7. A rotation signal generator 9 generates an ignition signal, corresponding to a predetermined ignition advance angle, which is applied to a waveform shaper 10, which, in turn, shapes the waveform of the ignition signal, and simultaneously controls the closing angle of an ignition coil 12. A switching circuit 11 interrupts or continues the energization of the ignition coil 12 in response to the output signal from the phase shifter 8. The output signal of the phase shifter 8 is also used for controlling the gate timing controller 4.
FIG. 2 shows a graphical diagram illustrating frequency vs. signal level characteristics of the output signal from the acceleration sensor 1. Here, a broken line curve A denotes the characteristics in a case where knocking does not occur, and a solid line curve B denotes the characteristics in a case where knocking does occur. The output signal from the acceleration sensor 1 includes a knock signal (a signal generated upon the occurrence of knocking), a mechanical noise of an engine, and various noise components carried on a signal transmission line such as an ignition noise, etc.
In comparing of the curve A with the curve B in FIG. 2, it is understood that the knocking signal has a defined distribution of specific frequencies. Various differences exist in the distribution due to difference in engines and/or differences in the mounting positions of the acceleration sensor 1. However, the main factor for the differences depends upon the presence or absence of knocking, and clear differences of the frequency distribution take place in accordance with the presence or absence of the knocking signal. Therefore, only frequency components of this knocking signal are passed to suppress the noise of other frequency components, thereby enabling a knock signal to be efficiently detected.
FIGS. 3 and 4 show the operating waveforms at various circuit points of the apparatus in FIG. 1, wherein FIG. 3 shows the various waveforms in a mode where no knocking occurs and FIG. 4 indicates the various waveforms in a mode where knocking takes place.
The operation of the conventional apparatus in FIG. 1 will now be described.
The rotation signal generated from the rotation signal generator 9 in response to the predetermined ignition timing characteristic due to the rotation of the engine is waveform-shaped to a switching pulse for providing a predetermined ignition angle by means of the waveform shaper 10 to drive the switching circuit 11 through the phase shifter 8, thereby interrupting or continuing the energization of the ignition coil 12. Thus, the engine is ignited and operated by the ignition voltage of the ignition coil 12 generated when the ignition coil 12 is de-energized. The vibration of the engine which takes place during the operation of the engine is detected by the acceleration sensor 1.
When no knocking occurs in the engine, the vibration of the engine due to knocking does not take place. However, the output signal of the acceleration sensor 1 contains a mechanical noise as shown in FIG. 3(a) due to other mechanical vibration or an ignition noise transmitted to a signal transmission line at an ignition time F. When the signal is passed through the frequency filter 2, the mechanical noise components of the signal are considerably suppressed as shown in FIG. 3(b), but since ignition noise components are high, the ignition noise components are passed through the frequency filter 2 in a high level. Thus, since the ignition noise is erroneously recognized as a knock signal in this state, the analog gate 3 closes its gate for a period t.sub.1 from the ignition time by the output (FIG. 3(c)) from the gate timing controller 4 triggered by the output from the phase shifter 8 to thereby block the ignition noise. Therefore, the output from the analog gate 3 contains only the mechanical noise at a low level as shown by the waveform I in FIG. 3(d). On the other hand, the noise level detector 5 responds to the variation of the peak value of the output signal (I in FIG. 3(d)) from the analog gate 3. In this case, the noise level detector 5 has a characteristic capable of responding to the relatively slow variation of the peak value of an ordinary mechanical noise and so generates a D.C. current slightly higher than the peak value of the mechanical noise. This is shown by the waveform II in FIG. 3(d).
Since the output from the noise level detector 5 is larger than the mean peak value of the output signal from the analog gate 3, the comparator 6 which compares both signals does not produce any output as shown in FIG. 3(e), and the noise signal is eventually eliminated. Therefore, the output voltage from the integrator 7 is zero as shown in FIG. 3(f), and the phase shifting angle (the phase difference between the input and the output) by the phase shifter 8 accordingly becomes zero. Thus, since the output from the phase shifter 8 is not shifted in phase, the opening or closing phase of the switching circuit 11 thus driven, i.e., the energizing or de-energizing phase of the ignition coil 12 becomes in-phase with the reference ignition signal from the waveform shaper 10, and the ignition timing coincides with the reference ingition position.
When knocking occurs, the output of the acceleration sensor 1 includes a knock signal component in the vicinity of a delay time t.sub.2 from the ignition time F as shown in FIG. 4(a), the frequency component of the output becomes the distribution as shown by the curve B in FIG. 2, and the signal passed through the frequency filter 2 and the analog gate 3 contains the mechanical noise largely superposed with the knock signal, as shown by the waveform I in FIG. 4(d). Since the rising portion of the knock signal among the signals passed through the analog gate 3 is abrupt as shown by the waveform I in FIG. 4(d), the rise of the output voltage of the noise level detector 5 is lagged or delayed in response to the knock signal. As a result, since the inputs from the analog gate 3 and the noise level detector 5 to the comparator 6 respectively become the waveforms I and II in FIG. 4(d), pulses as shown in FIG. 4(e) are generated at the output of the comparator 6. The integrator 7 integrates the pulses and generates an integrated voltage as shown in FIG. 4(f). Since the phase shifter 8 shifts in phase the output signal thereof and hence the reference ignition signal from the waveform shaper 10 shown in FIG. 4(h) in a direction for lagging the timing of the signal in response to the amplitude of the integrated voltage of the integrator 7, the phase of the output signal from the phase shifter 8 is lagged with respect to the reference ignition signal as shown in FIG. 4(g), and the switching circuit 11 drives the ignition coil 12 by this signal. Therefore, the ignition timing is lagged, and the knocking is suppressed. In this manner, the operating states shown in FIGS. 3 and 4 are repeated to provide an optimum ignition timing signal.
In U.S. Pat. No. 4,111,035, for the detection of the knock signal, a noise reference voltage is produced by the difference between the output of the band pass filter and the output of the low pass filter, and a comparator compares the output of the band pass filter with a reference voltage to detect the knock signal. In this case, the input of the low pass filter is obtained by the feedback output of the comparator.
An example of the supercharging characteristic of an internal combustion engine having a supercharger is shown in FIG. 5. In FIG. 5, the abscissa axis denotes the rotating speed of the engine, and the ordinate axis denotes the supercharging pressure of the engine.
In general, the supercharging pressure reaches a limited value P when the engine rotates at a speed faster than a rotating speed N (revolution per minute) as shown by the characteristic in FIG. 5, and also exhibits a rising characteristic in which the pressure does not reach the limited value P when the engine rotates at the speed equal to or slower than the rotating speed N. This rotating speed N is frequently set to approx. 2,500 r.p.m.
On the other hand, the engine is normally rotated in a practical rotating region of approx. 1,500 to 3,000 r.p.m. in the city driving mode, which is substantially in the rising region of the supercharging characteristic.
More particularly, the practical rotating range of the engine having a supercharger is in the rising region of the supercharging characteristic in FIG. 5 and hence in the rotating range where an increase in the output of the engine by the supercharger is low.
Since the delay in response by the supercharger is large in this rotating range, the rise of the rotating speed of the engine at the acceleration time is not abrupt, and the engine accordingly necessitates larger power. Therefore, the output of the supercharging characteristic in the rising region directly affects the acceleration performance of the engine.
In order to increase the power of an engine, it is preferred to set the ignition timing in the vicinity of the MBT, but if the ignition timing excessively approaches the MBT, knocking state occurs which may damage the engine. However, the ignition timing of the engine can be made to the MBT by setting the ignition timing during high speed rotation in a paractical rotation range as in FIG. 5, and the power of the engine can be increased by suitably designing the engine and the vehicle. In this case, a knocking thus occurred will not damage the engine and a decrease in an impression due to the knocking sound can be set to an allowable range.